Smear examination of peripheral blood for acid-fast bacilli (AFB) with sputum specimen collection
This test checks for the presence of *Mycobacterium tuberculosis* or other acid-fast bacteria in your blood or sputum. It helps diagnose infections like tuberculosis or other mycobacterial diseases.
["A blood or sputum smear test can detect certain serious infections that require prompt medical attention."]
Key facts at a glance
- LOINC
- 79424-8
- Short code
- Serial TB smears Pnl Spt Acid fast Stn
- Synonyms
- Serial TB smears Pnl Spt Acid fast Stn
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 7
- Ref high
- 56
- Critical range
- — – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- acid-fast-stain
- CPT
- 84484
- SNOMED
- 302773008
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test if you have symptoms like persistent cough, fever, night sweats, or unexplained weight loss. It’s also used in screening or diagnosing suspected tuberculosis, atypical mycobacterial infections, or other conditions where AFB are suspected in body fluids.
How the Test Works
A sample of your blood or sputum is collected and examined under a microscope. Acid-fast staining highlights certain bacteria, making them visible to detect if present.
Sample Collection and Preparation
For blood smears: A small blood sample is taken from your arm. For sputum smears: You’ll cough into a container, and your provider may guide you on proper collection techniques to avoid contamination.
What to Expect During the Test
Blood draws are quick and usually done in a clinic or lab. Sputum collection may require you to cough into a sterile container, sometimes with instructions to expectorate deeply. Results may take several days to weeks, depending on lab workload.
Reference range
Adult males: 7-56 U/L; Adult females: 7-43 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Positive results for AFB in blood or sputum strongly suggest an active mycobacterial infection, such as tuberculosis. Negative results do not rule out infection if the sample was insufficient or the bacteria are not acid-fast. Follow-up testing (e.g., culture or PCR) may be needed for confirmation.
Short name
AFB Smear (Blood/Sputum)
Frequently asked questions
How long does it take to get results?
Can I eat or drink before the test?
What if I have a negative result but still feel unwell?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy